Prostaglandin B-x is a short chain polymer of prostaglandin B. It is unique as a preservation agent in that it acts to protect mitochondria from the stress of an ischemic insult. In this polymerized form it appears not to possess any of the properties of the prostaglandin family from which it was derived. The drug is being tested as a potential agent for myocardial preservation on isolated hearts. The animal models being tested include both spontaneously hypertensive rats and Sprague-Dawley non-hypertensive rats. The preliminary data show activity of PBx at 38 degrees C in dosages of 80-120 mg per heart which resulted in a 50-70% functional recovery of the left ventricle after 40 minuts of ischemia. No controls (7) had any measurable recovery with this duration of ischemia.